kristen t. castaños · 2016. 2. 1. · kristen t. castaños stoel-rives january 13, 2016...

Kristen T. Castaños

Stoel-Rives

January 13, 2016

Groundwater Manganese in Land Application Areas

of 14

“about 0.65 mg/L”, and 0.05 mg/L, respectively. The CDO (paragraph 67) alleges biochemical oxygen

demand (BOD) overloading to the LAA as the cause of manganese in the groundwater.

Groundwater Chemistry for Manganese Mobilization

Iron and manganese are trace metals, found commonly in minerals, oxides, and hydroxides. Free iron and

manganese are typically solubilized into water under acidic (pH <8) and anaerobic conditions (reducing

environment) to form Fe2+

and Mn2+

(see Appendix A for Eh-pH stability diagrams). Iron and

manganese, in these forms, will persist until they reach aerobic environments, in which they will

precipitate out of solution, and typically complex onto soil surfaces.

Monitoring data from MW-7, MW-8, and MW-9 suggest a pH range of 7-8.5 in the groundwater. At this

pH range, and under anaerobic conditions, manganese will mobilize within an oxidation-reduction

potential (ORP) range of 0-0.3 V (Inglett et al. 2005). At the pH ranges found in the groundwater at the

Morning Star site, manganese has a higher potential to solubilize than iron.

Manganese Behavior in Groundwater Wells

A time-series plot of manganese in MW-7 is shown in Figure 1. Manganese ranges from non-detect to

2.20 mg/L, with 43% of values being reported as non-detect, less than the reporting limit (RL), or less

than the method detection limit (MDL). Between 2006 and 2011, manganese was consistently under the

MCLSEC; however, manganese concentrations exhibit an increasing trend beginning in August 2013;

samples collected in 2015 continued this trend.


Stoel-Rives

January 13, 2016


of 14

Figure 1. Time series for manganese concentrations in groundwater monitoring well MW-7. Non-detect or values less than the RL or MDL were reported as one-half of the RL or MDL, whichever was available.



than the method detection limit (MDL). Historically, manganese in MW-8 is highly variable between

sampling dates, and a discernible trend in manganese is not evident. However, similar to MW-7,

manganese concentrations began an increasing trend in August 2013, which continued through 2015.

0.00

0.50

1.00

1.50

2.00

2.501

2/1

/20

03

4/1

/20

04

8/1

/20

04

12

/1/2

00

4

4/1

/20

05

8/1

/20

05

12

/1/2

00

5

4/1

/20

06

8/1

/20

06

12

/1/2

00

6

4/1

/20

07

8/1

/20

07

12

/1/2

00

7

4/1

/20

08

8/1

/20

08

12

/1/2

00

8

4/1

/20

09

8/1

/20

09

12

/1/2

00

9

4/1

/20

10

8/1

/20

10

12

/1/2

01

0

4/1

/20

11

8/1

/20

11

12

/1/2

01

1

4/1

/20

12

8/1

/20

12

12

/1/2

01

2

4/1

/20

13

8/1

/20

13

12

/1/2

01

3

4/1

/20

14

8/1

/20

14

12

/1/2

01

4

4/1

/20

15

8/1

/20

15

12

/1/2

01

5

Man

gan

ese

Co

nce

ntr

atio

n (

mg/

L)

Sample Date

MW-7 Limitation (MW-7)

- Red squares indicate value reported as "ND"- Black circles indicate value reported as "<RL"


Stoel-Rives

January 13, 2016


of 14




than the method detection limit (MDL). Manganese in MW-9 has typically been at or near the MCLSEC of

0.05 mg/L; however, similar to MW-7 and MW-8, manganese began an increasing trend in August 2013,

which continued through 2015.

0.00

0.50

1.00

1.50

2.00

2.501

2/1

/20

03

4/1

/20

04

8/1

/20

04

12

/1/2

00

4

4/1

/20

05

8/1

/20

05

12

/1/2

00

5

4/1

/20

06

8/1

/20

06

12

/1/2

00

6

4/1

/20

07

8/1

/20

07

12

/1/2

00

7

4/1

/20

08

8/1

/20

08

12

/1/2

00

8

4/1

/20

09

8/1

/20

09

12

/1/2

00

9

4/1

/20

10

8/1

/20

10

12

/1/2

01

0

4/1

/20

11

8/1

/20

11

12

/1/2

01

1

4/1

/20

12

8/1

/20

12

12

/1/2

01

2

4/1

/20

13

8/1

/20

13

12

/1/2

01

3

4/1

/20

14

8/1

/20

14

12

/1/2

01

4

4/1

/20

15

8/1

/20

15

12

/1/2

01

5

Man

gan

ese

Co

nce

ntr

atio

n (

mg/

L)

Sample Date

MW-8 Limitation (MW-8)



Stoel-Rives

January 13, 2016


of 14


Manganese Limitations for MW-7 and MW-8

Manganese limitations for MW-7 and MW-8 were specified in the CDO as “about 0.175 mg/L” and

“about 0.65 mg/L”, respectively. These limitations, as presented in the CDO, uses the Sanitas

groundwater program, which used an historical mean of data prior to the issuance of the 2013 WDRs,

without a confidence interval. While these limitations may be appropriate, alternative manganese

limitations for MW-7 and MW-8 were computed in a similar manner to the Board’s approach; however, a

95% confidence interval was applied to an historical mean of the manganese data from samples collected

prior to issuance of the 2013 WDRs. Data values that were reported as non-detect, less than the reporting

limit (RL), or less than the method detection limit (MDL) were included in the statistical at ½ of the MDL

or RL. These limitations, and accompanying manganese exceedances in MW-7 and MW-8 are shown in

Table 1; both limitations are different than those specified by the Board in the CDO, with the limitation

for MW-7 being greater and the limitation for MW-8 less.

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.001

2/1

/20

03

4/1

/20

04

8/1

/20

04

12

/1/2

00

4

4/1

/20

05

8/1

/20

05

12

/1/2

00

5

4/1

/20

06

8/1

/20

06

12

/1/2

00

6

4/1

/20

07

8/1

/20

07

12

/1/2

00

7

4/1

/20

08

8/1

/20

08

12

/1/2

00

8

4/1

/20

09

8/1

/20

09

12

/1/2

00

9

4/1

/20

10

8/1

/20

10

12

/1/2

01

0

4/1

/20

11

8/1

/20

11

12

/1/2

01

1

4/1

/20

12

8/1

/20

12

12

/1/2

01

2

4/1

/20

13

8/1

/20

13

12

/1/2

01

3

4/1

/20

14

8/1

/20

14

12

/1/2

01

4

4/1

/20

15

8/1

/20

15

12

/1/2

01

5

Man

gan

ese

Co

nce

ntr

atio

n (

mg/

L)

Sample Date

MW-9 Limitation (MW-2,3,6,9)



Stoel-Rives

January 13, 2016


of 14

Table 1. Manganese exceedances for MW-7 and MW-8 for samples collected after the issuance of 2013 WDRs.

Monitoring Well Sample Date Manganese Concentration

(mg/L) Revised Limitation (mg/L) 1

MW-7 2/17/2014 0.27 0.2

5/12/2014 0.24 0.2

8/25/2014 0.26 0.2

11/13/2014 0.31 0.2

2/19/2015 0.31 0.2

5/18/2015 0.33 0.2

8/24/2015 0.69 0.2

11/12/2015 0.43 0.2

12/3/2015 0.383 0.2

MW-8 2/17/2014 1.18 0.56

5/12/2014 1.15 0.56

8/25/2014 1.33 0.56

11/13/2014 1.64 0.56

2/19/2015 1.73 0.56

5/18/2015 1.44 0.56

8/24/2015 1.34 0.56

11/12/2015 1.81 0.56

12/3/2015 1.98 0.56 1 Limitations for wells MW-7 and MW-8 were developed by summing the upper 95% confidence interval and the historical mean from each well, both calculated using data up to, and including, December 2013. Previous limitations, as stated in the CDO, were “about 0.175 mg/L” and “about 0.65 mg/L” for wells MW-7 and MW-8.

Manganese Limitation for MW-9

Manganese compliance in monitoring well MW-9 is assessed using the MCLSEC of 0.05 mg/L. MW-9 is

adjacent and downgradient to field MS1 (owned and operated by Gobel), on which rice was grown in

2014. However, as the Gobel field (MS-1) is now out of service as a LAA, MW-9 is likely upgradient or

cross-gradient. Investigations of the manganese behavior in MW-9 revealed a similar pattern to those

seen in MW-7 and MW-8, most notably the increasing trend beginning in August 2013. MW-9 appears

to be influenced by similar factors as MW-7 and MW-8, and thus, it is suggested that manganese

compliance in MW-9 be determined using current groundwater quality, as it is in MW-7 and MW-8. As

such, an alternative limitation for MW-9 was developed in a similar manner to those developed for MW-7

and MW-8, using an historical mean of data collected prior to issuance of the 2013 WDRs, with a 95%

confidence interval. Data values that were reported as non-detect, less than the reporting limit (RL), or

less than the method detection limit (MDL) were included in the statistical at ½ of the MDL or RL. The

limitation developed, and ensuing exceedances are shown in Table 2.


Stoel-Rives

January 13, 2016


of 14

Table 2. Manganese exceedances for MW-9 for samples collected after the issuance of 2013 WDRs.

Monitoring Well Sample Date Manganese Concentration

(mg/L) Revised Limitation (mg/L) 1

MW-9 8/25/2014 0.19 0.1

11/13/2014 0.32 0.1

2/19/2015 0.23 0.1

5/18/2015 0.34 0.1

8/24/2015 0.37 0.1

11/12/2015 0.45 0.1

12/3/2015 0.416 0.1 1 The limitation for well MW-9 were developed by summing the upper 95% confidence interval and the historical mean from, both calculated using data up to, and including, December 2013. The previous limitation was the MCLSEC of 0.05 mg/L.

Potential Sources of Dissolved Manganese in Groundwater

The CDO identified BOD overloading to the LAA in 2015 as the primary reason for manganese

concentration exceedances observed in monitoring wells MW-7, MW-8, and MW-9. While there may be

merit in this observation, it is not necessarily supported by manganese sampling data before 2015.

Specifically, this observation is not supported by the increases in manganese concentrations between 2013

and 2015, a time frame when BOD overloadings only occurred once on two fields in 2014. As such,

alternatives regarding the source of dissolved manganese in the groundwater monitoring wells should be

considered.

Drought Related Manganese Increases in Groundwater

Climate in California’s Central Valley has been highly variable in recent years. Currently, California is in

the fourth year of a severe drought. The drought has caused aquifers to diminish due to the reduction in

groundwater recharge via snowpack and surface water infiltration. In such circumstances, it is expected to

experience degradation of groundwater quality, as the volume rainwater that percolates for dilution and

oxidation is significantly less. Figure 4 shows a time series of manganese concentrations in monitoring

wells MW-7, MW-8, and MW-9, and the Sacramento Valley water year types during the data period, as

specified by California Department of Water Resources (DWR 2014). In the recent severe drought,

groundwater manganese concentrations in each well have increased significantly, when compared to

previous years.


Stoel-Rives

January 13, 2016


of 14

Figure 4. Manganese time series for MW-7, MW-8, and MW-9, and water year types.

Figure 5 shows the groundwater elevations for MW-7, MW-8, and MW-9 for water years dating back to

2004. It is evident that groundwater elevations in each well have decreased since 2013, to levels at or

near the record minimum. This indicates that aquifer volumes have decreased at the Morning Star site

during the same time period in which these wells began experiencing significant increases in manganese

groundwater concentrations. Therefore, it is possible that, due to the drought, manganese concentrations

in groundwater have increased due to less available groundwater volume for dilution. Figure 5 also

shows that there has been no evidence of increased net seepage from the cooling pond in terms of any

effects on shallow groundwater elevations in the LAA.

0.00

0.50

1.00

1.50

2.00

2.501

2/1

/20

03

4/1

/20

04

8/1

/20

04

12

/1/2

00

4

4/1

/20

05

8/1

/20

05

12

/1/2

00

5

4/1

/20

06

8/1

/20

06

12

/1/2

00

6

4/1

/20

07

8/1

/20

07

12

/1/2

00

7

4/1

/20

08

8/1

/20

08

12

/1/2

00

8

4/1

/20

09

8/1

/20

09

12

/1/2

00

9

4/1

/20

10

8/1

/20

10

12

/1/2

01

0

4/1

/20

11

8/1

/20

11

12

/1/2

01

1

4/1

/20

12

8/1

/20

12

12

/1/2

01

2

4/1

/20

13

8/1

/20

13

12

/1/2

01

3

4/1

/20

14

8/1

/20

14

12

/1/2

01

4

4/1

/20

15

8/1

/20

15

12

/1/2

01

5

Man

gan

ese

Co

nce

ntr

atio

n (

mg/

L)

Sample Date

MW-7 MW-8

MW-9 Limitation (MW-2,3,6,9)

Limitation (MW-7) Limitation (MW-8)

WY 2005 (AN)

WY 2004 (BN)

WY 2006 (W)

WY 2007 (D)

WY 2008 (C)

WY 2009 (D)

WY 2010 (BN)

WY 2011 (W)

WY 2012 (BN)

WY 2013 (D)

WY 2014 (C)


Sacramento Valley Water Year Types:Wet (W) - BlueAbove Normal (AN) - Light BlueBelow Normal (BN) - GreenDry (D) - OrangeCritical (C) - Red


Stoel-Rives

January 13, 2016


of 14

Figure 5. Groundwater elevations in wells MW-7, MW-8, and MW-9.

Manganese in Central Valley Aquifers

The California Rice Commission retained CH2MHILL and Plantierra to prepare the Rice-Specific Groundwater

Assessment Report on behalf of the Central Valley Regional Water Quality Control Board (CH2MHILL 2013).

Manganese was among the many constituents included in this report. The report found that “A USGS analysis

of the redox conditions of the shallow groundwater under the rice fields indicated that almost all of the wells

reported anoxic or reducing conditions in the groundwater…” The report also stated that manganese is a

naturally occurring trace element and is not applied in rice farming. Manganese concentrations in shallow

groundwater beneath rice fields were found well above the MCLSEC and values as high as 1.1 mg/L were

observed.

It is clear that even rice farming has the potential to cause elevated levels of manganese in shallow groundwater.

Rice is a common crop in the area surrounding the Morning Star site (see Appendix B). In addition, rice was

farmed on field MS1 in 2014, which may have impacted manganese concentrations seen in MW-9. Elevated

levels of manganese in shallow groundwater are not necessarily attributable to BOD loading on the LAAs and

may be consistent with other findings of elevated manganese concentrations is Central Valley shallow

groundwater.

68

70

72

74

76

78

80

82

84

86

Gro

un

dw

ate

r El

eva

tio

n (

ft)

Sample Date

MW-7 MW-8 MW-9


Stoel-Rives

January 13, 2016


of 14

Conclusions

Manganese concentrations in groundwater monitoring wells MW-7, MW-8, and MW-9 have increased

most notably since August 2013. The source of observed increases in manganese concentrations in these

groundwater wells is complex and could be attributed to causes unrelated to the LAAs. The CDO

attributes elevated levels of manganese in the groundwater to BOD overloading in the LAAs; however,

recent BOD overloading occurred primarily in 2015 (only 17 irrigation cycles out of 100 and the average

loading approximately 50 lb/acre/day), while increased levels of manganese concentrations in

groundwater was observed in each well beginning in 2013.

Evidence of drought related manganese concentration increases exists, in which aquifer volume has been

significantly diminished, leaving less groundwater volume available for dilution of manganese that

solubilizes into the groundwater. Groundwater elevations have decreased in recent years which

contribute to the diminished aquifer volume.

In addition, research for the Central Valley Water Board has identified anoxic or reducing conditions in

the groundwater below rice fields and the manganese concentrations can be elevated associated to the rice

farming. Rice farming is ubiquitous in and around Morning Star’s site. Increased levels of manganese

are likely influenced by the rice farming activities near Morning Star.

The increased levels of manganese concentrations in groundwater monitoring wells MW-7, MW-8, and

MW-9 is impacted by factors other than BOD loading. In order to return to compliance with the 2013

WDRs, it is appropriate to return to compliance with the BOD loading limitation for the LAAs, through

which manganese mobilization from the discharge will be minimized. However, the manganese trends in

groundwater suggest other factors, such as drought and nearby rice farming, will continue to influence

manganese concentrations at the Morning Star site. It is further recommended that MW-9 compliance be

determined similarly to MW-7 and MW-8.

References

CH2MHILL, Plantierra, July 2013. Rice-Specific Groundwater Assessment Report. Prepared for the

Central Valley Regional Water Quality Control Board. On behalf of the California Rice

Commission.

Department of Water Resources (DWR). 2014. Chronological Reconstructed Sacramento and San

Joaquin Valley Water Year Hydrologic Classification Indices. Retrieved from:

http://cdec.water.ca.gov/cgi-progs/iodir/WSIHIST.

Inglett, P.W., Reddy, K.R., Corstanje, R. 2005. Anaerobic Soils. In Encyclopedia of Soils in the

Environment. D. Hillel (ed). Academic Press. Pp. 71-78.

Reinhard, H.A., 2014. Groundwater Limitations Compliance Assessment Plan. Prepared for Morning

Star Packing Company, L.P.


Stoel-Rives

January 13, 2016


of 14

Appendix A

Eh-pH Stability Diagram for Manganese and Iron

Manganese

Iron

Appendix B

Map of Morning Star site and Surrounding Rice Fields

mileskm

36

Imagery Date: 7/10/2013

Rice fields are outlined in red.

CMoon

Polygonal Line

CMoon

Polygonal Line

CMoon

Polygonal Line

CMoon

Polygonal Line

CMoon

Polygonal Line

CMoon

Polygonal Line

CMoon

Polygonal Line

CMoon

Polygonal Line

CMoon

Polygonal Line

CMoon

Polygonal Line

CMoon

Polygonal Line

CMoon

Polygonal Line

kristen t. castaños · 2016. 2. 1. · kristen t. castaños stoel-rives january 13, 2016...

Documents